Radio frames in the Long Term Evolution (LTE) system comprises frame structures of a Frequency Division Duplex (FDD) mode and a Time Division Duplex (TDD) mode.
The frame structure of the FDD mode is shown in FIG. 1, in which, one radio frame with 10 ms is comprised of 20 slots each with a length being 0.5 ms and numbered with 0-19, and slots 2i and 2i+1 compose a subframe i with a length being 1 ms.
The frame structure of the TDD mode is shown in FIG. 2, in which, one radio frame with 10 ms is comprised of two half frames each with a length being 5 ms, one half frame comprises 5 subframes each with a length being 1 ms, and a subframe i defines two slots 2i and 2i+1 each with a length being 0.5 ms.
In the above two types of frame structures, for a Normal Cyclic Prefix (Normal CP), one slot comprises 7 Orthogonal Frequency Division Multiplexing (OFDM) symbols each with a length being 66.7 μs, wherein, a length of the CP of the first OFDM symbol is 5.21 μs, and the length of each of 6 remaining OFDM symbols is 4.69 μs; and for an Extended Cyclic Prefix (Extended CP), one slot comprises 6 OFDM symbols, and the length of the CP of each OFDM symbol is 16.67 μs.
A Multi-Broadcast Single Frequency Network (MBSFN for short) subframe can be used to transmit a Physical Downlink Shared Channel (PDSCH for short) and a Physical Multicast Channel (PMCH for short).
When the LTE system uses a Normal CP, one slot comprises 7 lengths of uplink/downlink OFDM symbols, and numbers of the OFDM symbols are 0, 1, 2, 3, 4, 5, 6 in turn in an order of transmitting time. When the LTE system uses an Extended CP, one slot comprises 6 lengths of uplink/downlink OFDM symbols, and numbers of the OFDM symbols are 0, 1, 2, 3, 4, 5 in turn in an order of transmitting time.
In the LTE system, the following three downlink physical control channels are further defined: a Physical Control Format Indicator Channel (PCFICH), a Physical Hybrid Automatic Retransmission Request Indicator Channel (PHICH), and a Physical Downlink Control Channel (PDCCH). Wherein,
(1) Information carried by the PCFICH is used to indicate the number of OFDM symbols in the PDCCH transmitted in one subframe, and is transmitted on the first OFDM symbol of the subframe, and a frequency position where it is located is determined by the downlink bandwidth of the system and a cell Identity (ID).
In the LTE R9 version, the Control Format Indicator (CFI) value can be configured with values 0, 1, 2, 3, 4 according to different subframe types.
(2) The PHICH is used to carry Acknowledge/Negative Acknowledge (ACK/NACK) feedback information of uplink transmission data. The number of the PHICHs and a time frequency position can be determined by system message in the Physical Broadcast Channel (PBCH) of the downlink carrier where the PHICH is located and the cell ID.
(3) The PDCCH is used to carry Downlink Control Information (DCI), which comprises: uplink, downlink scheduling information and uplink power control information. The formats of the PDCCH DCI (DCI formats) are divided into the following several types: DCI format 0, DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C, DCI format 1D, DCI format 2, DCI format 2A, DCI format 3 and DCI format 3A etc., wherein,
the DCI format 0 is used to indicate the scheduling of the Physical Uplink Shared Channel (PUSCH);
the DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C and DCI format 1D are used for different modes of code scheduling of a Physical Downlink Shared Channel (PDSCH);
the DCI format 2 and the DCI format 2A are used for different modes of spatial division multiplexing; and
the DCI format 3 and DCI format 3A are used for different modes of power control instructions of the Physical Uplink Control Channel (PUCCH) and PUSCH.
In the protocol of the version number of the LTE corresponding to Release 8 (R8), 6 types of bandwidths are defined as: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. The LTE-Advanced (Further Advancements for E-UTRA) is an evolved version of the LTE Release-8. Besides meeting or exceeding all related requirements of 3GPP TR 25.913: “Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)”, the requirements of the IMT-Advanced proposed by International Telecom Union-Radio (ITU-R) are also required to be achieved or exceeded.
Wherein, the requirements of backward compatibility with the LTE Release-8 refers to that a terminal of the LTE Release-8 can work in the network of the LTE-Advanced; and the terminal of the LTE-Advanced can work in the network of the LTE Release-8.
In addition, the LTE-Advanced should be able to work in frequency spectrum configurations with different sizes, comprising: a frequency spectrum configuration wider than that of the LTE Release-8 (for example, continuous frequency spectrum resources of 100 MHz), to achieve higher performance and the target peak rate. In consideration of compatibility with the LTE Release-8, for bandwidth greater than 20 MHz, a mode of carrier aggregation is used, i.e.,
two or more component carriers are aggregated to support downlink transmission bandwidth greater than 20 MHz;
the terminal can receive one or more component carriers at the same time according to the capability thereof.
According to the capability of carrier aggregation for the UE and interference circumstances as well as system load conditions, a UE-specific Downlink Component Carrier set (DL CC Set for short) can be configured through a high-layer signaling. When the system transmits downlink data to the UE, the PDSCH can be transmitted in any component carrier in the given DL CC Set.
A terminal of the LTE-A with a receiving capability of more than 20 MHz bandwidth can receive transmission on multiple component carriers at the same time. The terminal of the LTE Rel-8 can only receive transmission on only one component carrier, for example, the structure of the component carrier conforms to the Rel-8 specification.
At present, a way for transmitting the downlink control signaling, i.e., Physical Downlink Control Channel (PDCCH) in the LTE-Advanced standard comprises:
1) The PDCCH on one component carrier indicates the PDSCH resource of the same component carrier and the PUSCH resource of the uplink component carrier to which said component carrier is uniquely connected;
there is no carrier indicator field in the DCI format, for example, the structure of the PDCCH in the Rel-8 version (with the same encoding, the same CCE based resource mapping) and DCI formats.
2) The PDCCH on one component carrier can use the carrier indicator field to indicate the PDSCH or PUSCH resource of one of multiple component carriers.
A carrier indicator field of 3 bits is extended in the DCI formats of the Rel-8;
the structure of the Rel-8 PDCCH (with the same encoding, the same CCE-based resource mapping) is reused;
3) All the numbers of limiting blind detections under two modes are advisable.
4) Whether the Carrier Indicator (CI) field exists is semi-statically set.
When the PDCCH on one component carrier uses the carrier indicator field to indicate the PDSCH resource of another component carrier, if the UE detects falsely the PCFICH channel of the component carrier where the PDSCH is located, the UE judges the OFDM symbol starting from the PDSCH falsely and samples the data of the transmission carrier block carried by the PDSCH falsely, and the UE stores false data in the HARQ buffer and feeds back with the NACK, which will produce an error in the HARQ incorporation thereafter and have certain adverse effects on the performance of the system.
The component carrier set which can be cross-carrier scheduled for the UE is configured by the RRC signaling.
For the above cross-carrier scheduling case of the PDCCH on one component carrier indicating the PDSCH resource on another component carrier, if the CFI value of the component carrier where the PDSCH is located in such a case is determined according to the decoding of the PCFICH, the false detection of the PCFICH channel has adverse effects on the performance of the system.